1. Field of the Invention
The present invention relates to precursor compositions that are useful for the deposition of conductive electronic features. The precursor compositions can advantageously have a low conversion temperature to enable low-temperature treatment of the precursors to form conductive electronic features on a variety of substrates. The precursor compositions can also have a low viscosity to enable the deposition of the compositions using direct-write tools, such as ink-jet devices.
2. Description of Related Art
The electronics, display and energy industries rely on the formation of coatings and patterns of conductive materials to form circuits on organic and inorganic substrates. The primary methods for generating these patterns are screen printing for features larger than about 100 μm and thin film and etching methods for features smaller than about 100 μm. Other subtractive methods to attain fine feature sizes include the use of photo-patternable pastes and laser trimming.
One consideration with respect to patterning of conductors is cost. Non-vacuum, additive methods generally entail lower costs than vacuum and subtractive approaches. Some of these printing approaches utilize high viscosity flowable liquids. Screen-printing, for example, uses flowable mediums with viscosities of thousands of centipoise. At the other extreme, low viscosity compositions can be deposited by methods such as ink-jet printing. However, this latter family of low viscosity compositions is not as well developed as the high viscosity compositions.
Ink-jet printing of conductors has been explored, but the approaches to date have been inadequate for producing well-defined features with good electrical properties. For example, ink-jet printable conductor compositions have been described by R. W. Vest (Metallo-Organic Materials for Improved Thick Film Reliability, Nov. 1, 1980, Final Report, Contract #N00163-79-C-0352, National Avionic Center). The compositions disclosed by Vest included a precursor and a solvent for the precursor. These compositions were not designed for processing at low temperatures, and as a result the processing temperatures were relatively high, such as greater than 250° C.
U.S. Pat. Nos. 5,882,722 and 6,036,889 by Kydd disclose conductor precursor compositions that contain metallic particles, a precursor and a vehicle and are capable of forming conductors at low temperatures on organic substrates. However, the formulations have a relatively high viscosity and are not useful for alternative deposition methods such as ink-jet printing.
Attempts have also been made to produce metal-containing compositions at low temperatures by using a composition containing a polymer and a precursor to a metal. See, for example, U.S. Pat. No. 6,019,926 by Southward et al. However, the deposits were chosen for optical properties and were either not conductive or were poorly conductive.
U.S. Pat. Nos. 5,846,615 and 5,894,038, both by Sharma et al., disclose precursors to Au and Pd that have low reaction temperatures thereby conceptually enabling processing at low temperatures to form metals. It is disclosed that a variety of methods can be used to apply the precursors, including ink-jet printing and screen printing. However, the printing of these compositions is not disclosed in detail.
U.S. Pat. No. 5,332,646 by Wright et al. discloses a method of making colloidal palladium and/or platinum metal dispersions by reducing a palladium and/or platinum metal of a metallo-organic palladium and/or platinum metal salt which lacks halide functionality. However, formulations for depositing electronic features are not disclosed.
U.S. Pat. No. 5,176,744 by Muller discloses the use of Cu-formate precursor compositions for the direct laser writing of copper metal. The compositions include a crystallization inhibitor to prevent crystallization of copper formate during drying.
U.S. Pat. No. 5,997,044 by Behm et al. discloses a document, such as a lottery ticket, having simple circuitry deposited thereon. The circuitry can be formed from inks containing conductive carbon and other additives as well as metallic particles. It is disclosed that the inks can be deposited by methods such as gravure printing.
U.S. Pat. No. 6,238,734 by Senzaki et al. is directed to compositions for the chemical vapor deposition of mixed metal or metal compound layers. The method uses a solventless common ligand mixture of metals in a liquid state for deposition by direct liquid injection.
There exists a need for low viscosity precursor compositions for the fabrication of conductive features for use in electronics, displays, and other applications. Further, there is a need for precursor compositions that have low processing temperatures to allow deposition onto organic substrates and subsequent heat treatment. It would also be advantageous if the compositions could be deposited with a fine feature size, such as not greater than 100 μm, while still providing electronic features with adequate electrical and mechanical properties.
The ideal low viscosity precursor composition and its associated deposition technique for the fabrication of electronic features such as a conductor would combine a number of attributes. The conductive feature would have high conductivity, preferably close to that of a dense, pure metal. The processing temperature would be low enough to allow formation of conductors on a variety of organic substrates. The deposition technique would allow deposition onto surfaces that are non-planar (e.g., not flat). The conductive feature would have high resistance to electromigration, solder leaching and oxidation. The conductor would also have good adhesion to the substrate.
Further, there is a need for electronic circuit elements and complete electronic circuits fabricated on inexpensive, thin and/or flexible substrates, such as paper, using high volume printing techniques such as reel-to-reel printing. Recent developments in organic thin film transistor (TFT) technology and organic light emitting device (OLED) technology have accelerated the need for complimentary circuit elements that can be written directly onto low cost substrates. Such elements include conductive interconnects, electrodes, conductive contacts and via fills.